feat: close modals with browser back button on mobile (#257)

* feat: close modals with browser back button on mobile

Create reusable useModalHistory hook that pushes history state when a
modal opens and listens for popstate to close it. Apply to ReportModal,
ClearMissedConfirm, ExportModal, ImportConfirm, and all modals using
ConfirmModal/ShareDialog/Auth/ExportModal base components. Escape key
handling was already in place for desktop.

Closes #253

* fix: update tests for renamed button labels and missing useModalHistory mock

frontend/src/test/components/ReportModal.test.tsx

@@ -30,7 +30,7 @@ describe("ReportModal", () => {
 		render(<ReportModal isOpen={true} onClose={onClose} medications={[createMedication()]} />);
 
 		expect(screen.getByText(/report\.title/i)).toBeInTheDocument();
-		fireEvent.click(screen.getByRole("button", { name: /common\.cancel/i }));
+		fireEvent.click(screen.getByRole("button", { name: /common\.close/i }));
 		expect(onClose).toHaveBeenCalledTimes(1);
 	});